The present invention relates to a method and a device for the representation of an operation area during laser operations.
In ophthalmology, it is known in the case of poor eyesight to shape the cornea by the ablation of tissue. As methods, the so-called PRK (photorefractive keratectomy) and LASIK (laser-assisted in situ keratomileusis) methods have established themselves, in which initially a small flap of epithelium, Bowman membrane and stroma is cut and unfolded and then the PRK is carried out in the stroma bed.
Lasers of suitable wavelength are used for ablation. The excimer laser with a wavelength of 193 nm is particularly suitable for this purpose. However, other lasers such as Er:YAG solid-state lasers are also already used for this.
The data for the extent of the defective vision are established by sight tests, by means of refractometers and recently also by the evaluation of measurements of the wavefront. Other methods and devices are also known, which can be used to calculate firing coordinates for the actual operative procedure from these measurement values.
A laser operation is monitored by the surgeon or doctor usually by observing the operation area by means of a microscope. The doctor thus obtains a spatial impression of the operation area. However, the view through the microscope allows only one person a spatial impression.
Representation on a monitor etc. by means of a camera is also known. However, in this case the spatial impression of the operation area is lost. In the case of an operation using a slit scanner, the progress of the operation and the sequence of the ablation steps can be very well perceived and monitored by the doctor. The doctor can thus detect abnormalities in the ablation process early and counteract these, for example stop the operation, etc.
With today's modern spot scanners, the ablation process is no longer easy to understand due to various factors. Firstly, the firing frequency of the lasers is increasing all the time and lies well above the perceptive capability of the surgeon. The ablation process is also patient-dependent and the steering and placement of the spot in the ablation area is subject to complex algorithms which attempt to solve the most varied tasks and problems of the ablation process (thermal load, smoke). An ablation algorithm for example breaks down the necessary firings for a complete correction into many small individual corrections, with the aim that the operation can be aborted at any time and it can be guaranteed that an optically satisfactory result is achieved (cf. the valuable contribution to the state of the art in the patent specification DE 197 27 573). Therefore, in the case of more modern spot scanners, it is no longer possible for a surgeon to monitor the complex ablation process—by checking the correct positioning of the laser beam on the area to be operated on—by “looking through the microscope”.
The field of vision is also seriously limited when “looking through the microscope” because of the design. In order to use operation equipment, to ascertain status information or progress information for equipment, the doctor must stop looking through the operation microscope and therefore take his eyes off the operation area.
When representing the operation area for several observers (teaching purposes, monitoring etc.), the operation area can be represented by means of a camera and a monitor. Because of the principle involved, however, the spatial impression is lost in this case. However, this is of decisive importance during such microsurgical procedures.
The ablation processes in PRK using a spot scanner are so complex that the doctor is scarcely in a position to tell whether the operation is progressing correctly or to detect, early, problems which arise, so as to act to correct them. In order to control equipment etc., the doctor must take his eyes off the operation area, in order to use the equipment or to record status information.